U.S. Pat. No. 6,930,818 describes the microcup technology for forming a display panel. According to the patent, microcups may be formed by either a batchwise process or a continuous roll-to-roll process. A composition for forming the microcups is first coated on a substrate layer, followed by a microembossing or photolithographic method. A preferred process is microembossing by applying a male mold over the microcup composition to form microcups. The microcup composition can also be coated onto the male mold, followed by applying a substrate layer on top. The male mold may be released during or after the microcup composition is hardened.
The display panel formed is normally a very thin layer and therefore fragile. Once it is formed on a substrate layer, the microcup layer is very difficult to be peeled off from the substrate layer without causing damage to the structure.
Prior to the present invention, a release layer was considered to be added between a display panel and a substrate layer, to facilitate separation of the display panel, if needed, from the substrate layer after the display panel is formed on the substrate layer. However, this approach had its disadvantages. For example, the formation of the microcups by microembossing could become difficult. This is due to the fact that when pulling the mold from the partially cured microcups, with the presence of a release layer between the display panel and the substrate layer, the layers could be prematurely separated. Moreover, the mold could also get stuck in the partially cured microcups to cause permanent damage to the mold.
Another possible approach was to increase the thickness of the bottom of the microcups, so that the microcups can withstand the peel force for separating the display panel from the substrate layer and avoid causing damage to the display panel. However in this case, the thicker microcup bottom will cause more voltage drop at the microcup bottom, which likely leads to insufficient voltage for driving a display fluid contained within the microcups.
A further possible approach was to increase the thickness of the partition walls separating the microcups. However, increasing the thickness of the walls will decrease the fill factor, resulting in unsatisfactory optical performance.